Dismay; a warning device (5)
I believe the answer is:
alarm
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">dismay</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that dismay can be written as alarm)</span><br/ ><br/ >'<span class="explanation-format__original">a warning device</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for alarm that I've seen before include "Scare with warning device" , "Burglar deterrent" , "Feeling of fear" , "Flap" , "Put the wind up" .)